Rotary valves are well known in the art as a mechanism for introducing a flow of particulate material into a pressurized pneumatic conveying system. The pneumatic conveying system utilizes a flow of pressurized air through a pipe or tubular conduit to establish a fluidized flow of the particulate material fed into the conduit to move the particulate material from one place to another. The rotary valve has a housing defining an inlet opening at the top for the introduction of particulate material and a discharge opening at the bottom to discharge the particulate material flowing through the rotary valve into the pneumatic conveying system conduit. The housing rotatably supports an internal rotor for movement about a transverse, horizontal axis of rotation. The rotor is formed with a plurality of radially extending vanes that define chambers therebetween.
Preferably, the inlet opening has a triangular ridge at the throat of the opening projecting from the housing into the inlet opening. This triangular ridge creates an angular point of interaction with the rotor vanes rotatably moving within the rotor housing to direct particulate material to the sides and, thus, reduce pinch points defined between lines of the housing and the lines of the rotor vanes. Rotary valves without a triangular ridge structure will have a pinch point where the rotor vanes meet a parallel surface of the inlet opening. Rotary valves with the triangular ridge structure will ultimately have a pinch point where the rotor vanes cross a concave angular structure. Such pinch points can trap individual pellets of the particulate material between the housing and the rotor vanes and result in damage to the trapped pellets. Damaged pellets create undesirable fines within the flow of particulate material.
Each respective chamber receives a supply of particulate material when rotated to be opened to the upper inlet opening and then deposits the particulate material into the conduit when the chamber is rotated around the axis of rotation and opens to the conduit. The interior of the housing is, therefore, formed in a generally cylindrical shape so that the outer tips of the radially extending vanes pass in close proximity to the interior cylindrical surface of the housing to restrict leakage of pressurized air from the conduit around the rotor. The triangular ridge does create pinch points at the intersection of the triangular ridge and the periphery of the inlet opening. These pinch points do not result in much damage to the individual pellets as the angularly disposed triangular ridge intersects with the inlet opening to create an acute angle at the pinch point; nevertheless, individual pellets can become trapped at these pinch points.
Taiwan Patent No. M384858, granted to Yi-Ting Xie, et al, on Nov. 17, 2010, discloses the formation of a groove at each of the two pinch points created by the triangular ridge intersecting with the inlet opening in the housing. These grooves are formed as channels in the cylindrical surface of the rotor housing extending outwardly from the two aforesaid pinch points in line with the angle of the triangular ridge. The cross-section of the channel is depicted in FIG. 4 of Taiwan Patent No. M384858 and is formed as a rectangular channel having a proximal wall at the pinch point that is recessed into the cylindrical housing to allow relief from the pinch point and allow the passage of individual pellets of particulate material past the pinch point into the groove. The distal wall of the channel defines a depth of the channel into which particulate material can accumulate. The overall depth of the groove channel is substantially uniform from the proximal wall to the distal wall.
In U.S. Pat. No. 5,381,933, issued to Walter Beirle, et al., on Jan. 17, 1995, a rotary valve for transferring particulate material is disclosed with a baffle structure located within the throat of the inlet opening. The baffle structure in the Beirle patent creates pinch points where the baffle intersects with other side structure of the inlet opening. To provide a relief for the particulate material getting trapped in these pinch points, the Beirle patent provides a pair of grooves oriented in alignment with the side structure and positioned beneath the baffle structure. The Beirle grooves meet at an apex which is located in the center of the rotary valve.
In operation, the passage of the rotor vane past the proximal wall can establish an eddy current of air behind the proximal wall to restrict the use of the depth of the channel at the proximal wall. Furthermore, the uniform depth of the groove channel can result in the compaction of particulate material at the distal wall. If the particulate material compacts at the distal wall, the sweeping movement of the rotor vanes will not effect a deflection of the individual pellets into the groove channel, resulting in the pellets getting trapped between the top of the distal wall and the rotor vane. Furthermore, fines can accumulate in the ceiling of the groove channel to present a difficult cleaning problem when the rotary valve is used in conjunction with a new particulate product.
Accordingly, it would be desirable to provide a rotary valve that further reduces the creation of fines in the transfer of particulate material into a pneumatic conveying system connected to the rotary valve.